<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<form method="post" action="/user/save">
    <label for="id">Id</label>
    <select name="id" id="id">
        <option value=""></option>
        <option th:each="user:${users}" th:value="${user.getId()}" th:text="${user.getId()}"></option>
    </select>
    <label for="name">Name</label>
    <input name="name" id="name">
    <label for="age">Age</label>
    <input name="age" id="age">
    <input type="submit" value="Submit">
</form>
</body>
</html>